This invention relates to a new and distinctive broccoli inbred line, designated KI-13.
There are numerous steps involved in the development of any new and novel, desirable plant germplasm with superior combining ability. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals and the best breeding method to reach those goals. The objective is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important characteristics may include higher yield, better flavor, improved color and field holding ability, resistance to diseases and insects along with economic seed yields to facilitate the cost of hybrid seed production.
The method chosen for breeding or selection depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the cultivar (variety) used commercially (e.g. F.sub.1 hybrid, pureline). The complexity of inheritance influences the choice of breeding method. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, observation in multiple locations and seasons provide a better estimate of its genetic worth.
The development of commercial broccoli hybrids requires the development of homozygous inbred lines. Breeding programs combine desirable traits from two or more germplasm sources from which various broad based breeding gene pools are used to develop inbred lines by self-pollinating followed by selection of desired phenotypes sometimes utilizing anther, microspore and ovule culture to speed up and improve selection efficiency.
Description of breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g. Allard, "Principles of Plant Breeding", 1960; Frey, "Plant Breeding II", 1981; Tsunoda, et. al., "Brassica Crops and Wild Allies", 1980).
Proper testing and evaluation should detect any major faults and establish the level of superiority or improvement over current cultivars (varieties). In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. For seed-propagated cultivars (varieties), it must be feasible to maintain the inbred lines and produce seed easily and economically.
Broccoli is a new crop in North, South and Central America, Europe and Asia. The introduction of hybrid cultivars in the 1960's provided a magnitude increase in yield, holding ability, expanded growing seasons and large scale production of broccoli. The goal in broccoli breeding is to make continued improvement in hybrid broccoli yields and horticultural characteristics in order to sustain the supply to meet continuous increase in demand for broccoli in developed and emerging world economies. To accomplish this goal new breeding methods such as anther culture and microspore culture have been utilized to more rapidly generate inbred broccoli lines from more diverse germplasm sources.
Broccoli (Brassica oleracea, Italica group) belongs to the mustard family. All Brassica oleracea will cross pollinate. Pollination is effected by insect vectors, most common of which is the honey bee. Broccoli, like most other brassica, have a genetic characteristic of self incompatibility which encourages cross pollination resulting in higher levels of variability. Variability in populations is desired for wide adaptation and survival. Broccoli breeding populations can be inbred for 8 to 9 generations and/or use doubled haploids derived from anther culture to develop homozygous inbred lines. Broccoli F.sub.1 hybrids can be produced by using self-incompatibility or cytoplasmic male sterility to control pollen movement between selected inbred lines.
Self-incompatibility is a breeding system that enforces out-crossing and therefore maximizes recombination in cross pollinated species. This breeding system in nature has been utilized by man in F.sub.1 hybrid breeding, especially in brassica vegetables (Tsunoda et al, 1981, chapter 13). The stigma of brassica flowers is the site of the incompatibility reaction. Compatible pollen tubes pierce the cuticle layer of the stigma and grow down the style tissue. When incompatible pollen grains germinate on the stigma, some pollen tubes can penetrate the cuticle layer but the penetrated tubes can not grow down the style. "Bud pollination" is done to overcome the self-incompatibility in order to maintain inbred broccoli lines. Young buds of inbred broccoli and other brassica can be fertilized by incompatible (self) pollen. Unlike mature stigmas, the young stigmas cannot discriminate between compatible and incompatible pollen. Therefore bud pollination by hand will produce selfed seed on inbred broccoli, thereby maintaining the self-incompatibility needed for hybrid seed production.
Male sterility is another method used in brassica vegetable species to produce F.sub.1 hybrids. This method of producing hybrids in Brassica is a more recent development compared to self-incompatibility.
The plants associated with the Brassica group have been familiar to mankind since ancient times, and have always been of great agricultural importance. Brassica is a major food species world wide. Brassica species have a general adaptation for cool climate growing conditions. Therefore adaptation has occurred in summer growing conditions with cool to moderate climates and to winter growing conditions in warmer or tropical locations.